Photo-exposure meter.



s. PRATT.

PHOTO EXPOSURE METER.

APPLICATION FILED JUNE 3..1911.

Patented Sept. 24, 1912.

mvsuron amp/na fiazt SEDGWICK PRATT, OF PIEDMONT, CALIFORNIA.

PHOTO-EXPOSURE METER.

Specification of Letters Patent.

Patented Sept. 24, 1912.

Application filed June 8, 1911. Serial Nd. 631,018.

To (451 irb 01/1- 1' 15 may concern Be it known that I, SEDGWICK PRATT, a citizen of the United States, and 'aresident of Piedmont, in the county of Alameda and State of California, have invented a new and Improved Photo-Exposure Meter, of which the following is a full, clear, and exact description.

This invent-ion relates to a new and irnproved meter for determining the length of time of exposure which is necessary to obtain a photograph showing the proper detail of an object.

If there is interposed between the eye and an illuminated oli'ect, light screens, such as pieces of transparent colored glass, so as to just obscure the light t'rom the object, and the correct time of exposure of a photographic plate or film for such illuminated object, under such conditions, be ascertained. then a scale of exposure can be compiled for objects of various degrees of illumination: thus, if eachscreen obscures 5054 of? the light from the object, then the light transmitted to a second screen will be .70; of that coming to the first screen, and this second screen willtransmit of this light to a third screen, and so on for any number of successivescreens. The stronger the illumination of the object, the more screens it will be necessary to interpose between the eve and the object, in order to ob scure the light, and the less will be the exposure in length of time. If one sort-en obscures the light from the objeotpantl jt'he time of exposure for this objectis onds, then the time of exposure for an objectwhose light is obscured by two of-such screens would be 50% of 80 seconds, f r-4Q seconds. and where three screens are required, the time of exposure will be 50% of 40 seconds, or 20 seconds, and so on.

It is therefore an object of this invention to embody the above feature in a meter, whereby, by exposing successively any number of light screens between the object and the eye, until the properdegree of obscring is obtained, the interposition of screens being in synchronism will. c movement of an indicator or pointer, running along a pie-calculated scale, the times of exposurecan be readily read oil on this scale for difierent degrees of illumination of the object to be photographed, and for different apertures A further object of this invention is to providea photographic'meter which will be simple in'construction, inexpensive to manu- 1s a vertical transverse section taken on line 3 3 of Fig. 4; and Fig. 4 is a vertical longitudinal section taken on line H of Fig. 3.

Referring more particularly to the separate parts of thisinvention as embodied in the form shown in the drawings, 1 indicates a casing, which may be or any suit-ableform, and is shown in this instance to be provided with a body portion2 and heads 3 and 4 connected to the bodyportionLin any suitable manner.

The casing 1 preferably has an opening 5, whereby access to-the interior may be had, and this opening is normally closed by a cover 0, which projects overthe margin of the opening slightly, where it is locked in position by screws 7. These/screws, it will be noted, are cut otf for half of their heads, so that. they can be revolved to a position the cut--'ofl port-ions are faced, toward each other, so that the cover ca'n be readily inserted over the opening 5', and alsojso that after the coverfhasbeen once'inserted, the projecting portions of the head screws can be rotated over thee-over, to secure it in position. One' ofthe heads 3 is provided with an aperture 8, which-may be pointed toward the object of which it is desired to talce a picture, and the other of the heads 4 may be provided with an opening 9, which may be termed the eyepiece, and through which the user can look in observing an object. The aperture -8 ant;l theopening 9 may be provided respectiv y. with shutters l Vithin the casing 1, there is provided means for supporting a plurality of screens casing 1. The rack may be provided with legs 17, for properly supporting it within the casing 1. A

The. screens 14 may be of any suitable character, such that they will be transparent to light and yet absorb some of the "ays of the light, and colored glass has been found to be suitable for this purpose. It will be noted that the screens 14: project through the slots 16, so that they extend beyond one of the sides at least of the rack 15, so that they can be supported in a raised position out of contact with the bottom of the rack, by means of a controller 18, which is shown in the form -of a strip of metal sliding-1y mounted in an opening 19 in one of the heads 3, and provided at its outer end with a tab or fing'cnhold 20, whereby it can be readily grasped between the linger and thumb and slid baclrand forth. It is to be noted that the inner end of the controller 18 is provided with a cut-out portion, indicated at il, which forms a drop, permitting the glass or other form of lightscrccns to fall from their raised position to their lower position, that is to say, when the rear end of the highest portion of the controller 18 passes from under each screen successively, it is permitted to drop to such a position that it rests on the bottom margins of the slots 16.

Inasmuch as the lower position of the screens 14 brings them in such a position that they will cut the line of ligl-it passing vfrom the aperture 8 to the eyeopcning 9, they will obscure to a greater'or less extent, depending on the number of screens lowered, the light coming from the object being looked at, to the eye. The movement of the controller, and thus the number of screens cutting the lineiof sight bctwccn'thc apcu tures S and 9, is indicated by a pointer secured to the controller in a position to the rear-of the drop in the controller. that it will correspond to the position of the last lowered screen. This pointer projects through a slot 23 provided in the asino 1. and is adapted to indicate on procainelated scale 25 located on the casing: l. the time of exposure necessary for different. stops, that is to say,'ditferent-sizcd apertures v in the camera, to obtain a photograph of an 12.5 means object, with the degree of detail desired, with a particular stop, and with a particular degree of illumination of the object. The scale 25, as shown, is divided into columns of figures arranged longitudinally and transversely of the casing, in a graded manner and according to a predetermined calculation based on actual trials with the instrument, and represents the times in seconds and fractions of a second necessary for various stops, to obtain the degree of detail necessary with different degrees of illumination, of the object to be photographed.

It will be seen that the longitudinal columns are headed at one end by the numerals "2, 4t, 8. 16, 32, and 61, which represent the numbers of the stops corresponding to various-sized apertures under the U. S. or

uniform system. At the opposite side of the scale, are figures 5.(, S, 11.3, 16, and which represent the number of the stops of various magnitudes, or focal system. 7

It is to be noted that the scale 25 is divided by a zig-Zag line, indicated at 26, into two sections. and in the actual instrument, these sections are further distinguisl'ied by having the portion to the left of thezig-zag line in colored numerals. and the portion to the rightof the Zig-zag line in black numerals. It-has been endeavored to bring-out this distinction by making the numerals to the right of the Zia-sag line somewhatheavier than those to the left of the zigaag line. This partition is made in order (0 distinguish between the different sections of.

time on the different parts of the scale: that is to say, the light figures indicated to the left of the Zig-Zag line represent the time in seconds, and the black numerals or those to the right of the zig-Zag line, indicate thot iine in fractional parts of a second; thus a black of a second. and a block 300 means I oi a second. and so on. A light 1.3; that is to say, to the left of the zigf-zag' line, means 1.3 seconds, and so on. For the purpose of lockingthe controller 18 in its in- IlQl'HlOSf position, when not in use. the shuttcr 10. which closes the front aperture S.-is provided with a locking lug or extension 27. which is adapted to engage in a correspondin; slot 23 in the controller 18.

The utility of the device will be readily understood when taken in coniic-"tion "with the above description; lVhen it is desired to lake 1. photograph of an objec and the cll'ect of the light on this particular objtut is desired to be ascertained. 3 hat the time of cxposure'in using the camera for any particular stop can be calculated. the open- .112" t) is hold in juxtaposition to the eve. and the opening 8 directed toward the object. "The controller 18 is then drawn out gradually. so that the colored light-absorbing screens 14 drop down one by one across the according to the 1M? line of sight between the users eye and the object. when a suflicient number of screens have fallen to make the detail on the object visible to the extent desired, the movement of the controller 18 is stopped, and the scale 25 referred to, so as to ascertain what column on the scale is indicated by the pointer W'e will assume that We are using a camera, and desire to use an aperture corresponding to the stop 4: in the uniform system. and that the pointer stopped at the sixth column, as indicated in Fig. 1. The time of exposure necessary, then, will be 2.5 of a second in order to obtain the proper detail with this particular stop in use on the camera, and in taking the particular object viewed through the meter. In order to reset the meter, it is merely necessary to reverse the same; that is to say, turn it upside down, and force the controller back into the casing 1.

While I have shown one embodiment of my invention, I do not wish to be limited to the specific details thereof, but desire to be protected in various changes, alterations and modifications which may come within the scope of the appended claims.

Having thus described my invention, I claim as new and desire to secure by Letters Patent 1,. The combination with a casing having a line of sight therethrough, of a plurality of independent light-absorbing screens disposed in said casing above and tending to drop of their own weight into, the path of the line of sight, and a controller engaging said screens to hold the same out of the path of the line' of sight, said controller being movable to successively disengage from said screens.

2. The combination with a casing having a line of sight therethrough, of an arm extending inwardly of the casing, a plurality of light-absorbing screens independently supported on said arm in a series superiacent the path of the line of sight, said arm being movable outwardly of the casing and from beneath the screens, whereby to permit the latter to successively drop into operative position.

The combination with a casing having a scale and a plurality of apertures therein harming a line of sight through the casing, of light screening means comprising a plurality of independent movable members adapted to obstruct a graded manner the passage of light along said line of sight, a movable controller for said screening means for controlling the movement of said members successively across the line of sight, and a pointer movable consentaneous with said controller and cooperating with said scale to indicate the degree of obstruction of light by said screening means.

4. The combination with a casing having a line of sight therethrough, of an arm extending inwardly of the casing, a plurality of light absorbing screens independwhereby to permit the latter to successively drop into operative position, and means to lock said arm in its innermost position whereby to maintain all of the screens in inoperative position.

5. The combination with a casing having a line of sight therethrough, of a plurality of light-absorbing screens movably mounted in said casing, so as to be capable of moving into and out of the path of said line of sight. and a controller normally engaging said screens to hold the same in an inoperative position? and movable to successively disengage from, and release, the same.

6. The combination with a casing having a line of sight therethrough, of a plurality of light-absorbing screens movably mounted in said casing, so as to be capable of moving into and out of the path of said line of, sight, a controller for regulating the movement of said screens, the said casing being pro-- vided with a scale, divided into units of time corresponding to different apertures, and a pointer operated by said controller, adapted to indicate on said scale divisions of time corresponding to the number of screens crossing the path of said line of sight.

7. The combination with a casing having a plurality of apertures therein through which a line of sight is formed extending through the casing, of a rack in said casing,

having a plurality of slots therein, light screens movably mounted in said slots, and a controller for supporting said screens in a raised position above said line of sight and movably mounted in said casing, so as to permit said screens to fall one by one across said line of sight.

8. The combination with a casing having a plurality of apertures therein through which a line of sight is formed extending through the casing, of a rack in said casing, having a plurality of slots therein, light screens movably mounted in said slots, and a controller for supporting said screens in a raised position above said line of sight and movably mounted in said casing, so as to permit said screens to fall one by one across said line of sight, said rack having its sides flaring outwardly so as to permit the insertion of said screens in said slot.

9. The combination with a casing having a plurality of apertures therein through which a line of sight is formed extending through the casing, of a rack in said casing, having a plurality of slots therein, light screens movably mounted in said slots, a

wntmller for summ t-ting said screens in a I rnii 0 i pmitim: iilJOV said line of sight and l movably mounted in said casing, so as to I permit said screens to fall one by oneacross said line of sight, said casirfg having, an I opening in the top thereof, a cover detach-- ably connected to said casing, for closing said opening, and means for locking said rover in closed position on said casing.

10. The cembination with a casing having a plurality of openings therein extending in allnenient w'th each other to form a line of sight, of a rack in said casing, stamped from a. single sheetof metal, having sides extending parallel to each other and flaring l l outwardly at their upper ends, said sides having verlicallpdisposed slots ihera-imsziid rack having legs projecting frum the bottom thereof, colored glass screens movably mounted in said slots, and a controller mava'bly Fnounted in said casing and adapted to support said screens out of al inement with said opening and adapted to permit said screens to fall across said line of sight in a gradual manner.

In testimony whereof I have signed my name to this specification in the presume of two subscribing Witnesses.-

' SEDGVVICK PRATT.

Witnesses HARRY A. KUNZ, W. J. M.

Copies of this patent maybe obtained for five cents each, by addressing the Gommissizmer of Patents,

Washington, D. G. 

